Conventionally, cellular systems operate in licensed spectrums in which a base station (BS) and one or more wireless devices may communicate through a wireless spectrum licensed to a wireless operator. Cellular network communication systems have been expanding their usage to unlicensed spectrum, which is also known as open spectrum or free spectrum. Some examples of the unlicensed spectrums are the Industrial, Scientific, and Medical (ISM) Band, the Unlicensed National Information Infrastructure (UNII) band, other unlicensed or shared spectrums, and so forth. Different countries may normally have different unlicensed spectrums as the regulations in each country might be different from other countries. The potential uses of unlicensed spectrums of LTE have gathered attentions of telecommunication equipment vendors and operators. One of the reasons for the recent attentions is because of the limited availability of licensed spectrums. In order to provide high throughput service to more users, LTE may resort to utilizing unlicensed spectrums for communications.
One of the major challenges is to operate the cellular system in an environment of uncertainty. As communications are conducted within the domain of unlicensed or shared spectrums, there could be other communication devices that would also like to use unlicensed or shared spectrums. These communication devices may belong to the same or different radio access technologies. For example, wireless communication operations that are normally conducted within the spectrums reserved for Long Term Evolution (LTE) wireless communication system may prefer to co-exist with Wi-Fi radios in the free spectrum that is normally used by Wi-Fi radios. However, within the unlicensed band, a LTE device might not be able to freely transmit or receive at any given time because of limitations related to spectrum sharing. This problem would not exist in a convention cellular LTE system in which the transmission and reception operations are normally scheduled and would not conflict with operations that occur in the free spectrum.
In order to cope with the uncertainty of transmitting and receiving opportunities in the unlicensed spectrum, a free spectrum sharing method could be devised such that wireless communication devices that normally use the license spectrum may utilize a free spectrum without conflicting with devices that normally use the unlicensed spectrum.
For general information related to licensed-assisted access to unlicensed spectrum, technical specification 3GPP TR 36.889 V0.3.1 dated February 2015 titled 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on Licensed-Assisted Access to Unlicensed Spectrum; (Release 13) contains definitions to concepts and teens and is hereby incorporated by reference. For further information related to licensed-assisted access or licensed-assisted carrier aggregation in unlicensed spectrum, 3GPP TSG RAN WG2 #89 R2-150234 titled Scenarios and Requirements for LAA may also contain related concepts and terms and is hereby incorporated by reference.